Networking Study
Guide
For
MCSE Examinations
1
Module 1
Introduction to Hardware
The interior of a computer looks very complicated at first glance. When the case
is removed there is a mass of bits, cables and components that can intimidate
the uninitiated. This lesson will seek to dispense some of the mist that may
surround the hardware of a computer.
Motherboards
The most important part of any computer is the motherboard. As the name implies a motherboard
is the mother of all other components in a computer.
The motherboard brings all the core components together such as the Central Processing Unit
(CPU), Memory and Hard Disks. In short, the motherboard connects and allows all of the
components in the computer to work together.
There are two different types of Motherboard: AT style and ATX style.
AT Motherboards
The AT-style motherboards represent the classic approach to component placement. ATmotherboards are available in two variations, the baby AT and the full AT. Both variations
simply refer to the overall dimensions of the board.
AT Boards are generally found in older systems, typically those that use the now aged Pentium
Processor. The Majority of AT motherboards had a single keyboard port soldered to the
motherboard
The I/O ports (e.g. USB, COM and PS/2 ports) are separate from the motherboard and are placed
on a riser card or separate headers.
To identify an AT motherboard, first check the power connectors. AT Motherboards use two sets
of 6
Caution it is possible to plug these connectors in the wrong order and fuse the motherboard
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ATX Motherboards
The ATX-style motherboards are a result of the industry’s push for standardization and are found
in most systems today. Most modern computers contain an ATX motherboard. ATX boards can
use Advanced Power Management.
Distinguished by ATX boards
having more than have Keyboard
just one external
connector
Mouse
Serial
Parallel and
USB connectors.
ATX boards can also be distinguished by the mono-block power connectors. Also available in
micro ATX enabling the use of smaller cases.
Motherboard Components
There are two types of receivers for CPU’s
Zero insertion force or ZIF sockets. With a ZIF socket, before the CPU is inserted, a lever or
slider on the side of the socket is moved, pushing all the sprung contacts apart so that the CPU
can be inserted with very little force (generally the weight of the CPU itself is sufficient with no
external downward force required). The lever is then moved back, allowing the contacts to close
and grip the pins of the CPU, often with a fan attached for cooling.
Single Edged Contact (SEC) cartridge slot or Slot 1 seen on PII and PIIIs. Developed by Intel to
add Cache memory for the processor cheaply. The processor is mounted on a Single Edge
Connector Cartridge (SECC), much like a PCI slot, but with a 242-lead edge-connector.
Bridges
There are two main bridges on a motherboard the Northbridge and the Southbridge.
Purpose of Bridges: Bridges control access to the processor from the peripherals.
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The Northbridge, also known as the Memory Controller Hub (MCH), is traditionally one of the
two chips in the core logic chipset on a PC motherboard. The Northbridge typically controls
communications between the CPU, RAM, AGP or PCI Express, and the Southbridge. A
Northbridge will typically work with only one or two classes of CPUs and generally only one
type of RAM. There are a few chipsets that support two types of RAM (generally these are
available when there is a shift to a new standard).
The Southbridge, also known as the I/O Controller Hub (ICH), is a chip that implements the
“slower” capabilities of the motherboard in Northbridge Southbridge chipset computer
architecture. The Southbridge can usually be distinguished from the Northbridge by not being
directly connected to the CPU. Rather, the Northbridge ties the Southbridge to the CPU. The
functionality found on a contemporary Southbridge includes; PCI bus, ISA bus, SMBus, DMA
controller, Interrupt controller, IDE, (SATA or PATA) controller ,LPC Bridge, Real Time Clock,
Power management (APM and ACPI) and Nonvolatile BIOS memory
BIOS Chips
The [BIOS (Basic Input Output System)] refers to the software code run by a computer when
first powered on. The primary function of BIOS is to prepare the machine so other software
programs stored on various media (such as hard drives, floppies, and CDs) can load, execute, and
assume control of the computer. This process is known as booting up.
The BIOS is stored as a ROM (Read-Only Memory) program and is retained when the machine
is turned off. Settings within the BIOS may be changed by the user and these changes are stored
in the BIOS memory this is maintained by a trickle of charge from the BIOS battery.
Memory
SIMMS- Single Inline Memory Modules. An older type of memory only seen on very old
motherboards came in 30 pin modules and 72 pin modules.
SDRAM chips are rated according to their maximum clock rate and their read cycle time.
Common clock ratings include 66MHz, 100MHz, and 133MHz. Common read cycle times
include 50ns and 60ns.
DDR SDRAM or double-data-rate synchronous dynamic random access memory is a type of
memory integrated circuit used in computers. It achieves greater bandwidth than ordinary
SDRAM by transferring data on both the rising and falling edges of the clock signal (double
pumped). This effectively nearly doubles the transfer rate without increasing the frequency of the
front side bus.
Stick/module specification
PC-1600: DDR-SDRAM memory module specified to operate at 100 MHz using DDR-200
chips, 1.600 GByte/s bandwidth
PC-2100: DDR-SDRAM memory module specified to operate at 133 MHz using DDR-266
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chips, 2.133 GByte/s bandwidth
PC-2700: DDR-SDRAM memory module specified to operate at 166 MHz using DDR-333
chips, 2.667 GByte/s bandwidth
PC-3200: DDR-SDRAM memory module specified to operate at 200 MHz using DDR-400
chips, 3.200 GByte/s bandwidth
Drive Connectors
Integrated Device Electronic (IDE)
[Integrated Device Electronic (IDE)]] connectors connect the motherboard, via a ribbon cable to
various peripherals, the most common being hard drives and CD ROMs. On most boards there
are 2 channels/connectors, each can have 2 devices attached giving a total of four IDE devices.
If one device is attached to a cable, it should be configured as the master. If two devices are
attached to the same cable then one must be the master device and one the slave. Master and
slave are configured by the use of jumpers. Jumpers are small, insulated sleeves with a contact
inside used to complete a circuit
Hard Disks
Hard disks are used to store data in a non-volatile form within the machine. I.e. the data remains
intact even if the power to the device is cut off. Data is stored as magnetic ones and zeros on a
steel platen and is read by pickup arms that scan the drive as the platens spin.
Most major hard drive and motherboard vendors now support self-monitoring, analysis, and
reporting technology (S.M.A.R.T.), by which impending failures can be predicted, allowing the
user to be alerted to prevent data loss.The mostly sealed enclosure protects the drive internals
from dust, condensation, and other sources of contamination. The hard disk’s read-write heads
fly on an air bearing which is a cushion of air only nanometers above the disk surface. The disk
surface and the drive’s internal environment must therefore be kept immaculate to prevent
damage from fingerprints, hair, dust, smoke particles, etc., given the submicroscopic gap
between the heads and disk.
Floppy Disks
The floppy disc controller is generally situated near the IDE controllers and in fact looks like a
small IDE slot
The ribbon has a twist and the first floppy drive (A: drive) should be placed after the twist if the
cable has more than three connectors. If the cable is really old it may have a connector for a 5 1/4
Floppy drive.
SCSI
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SCSI stands for “Small Computer System Interface”, and is a standard interface and command
set for transferring data between devices on both internal and external computer buses. SCSI is
most commonly used for hard disks and tape storage devices, but also connects a wide range of
other devices, including scanners, printers, CD-ROM drives, CD recorders, and DVD drives. In
fact, the entire SCSI standard promotes device independence, which means that theoretically
SCSI can be used with any type of computer hardware.
On a parallel SCSI bus, a device (e.g. host adapter, disk drive) is identified by a “SCSI ID”,
which is a number in the range 0-7 on a narrow bus and in the range 0-15 on a wide bus.
SATA
Serial ATA (SATA) is a computer bus technology primarily designed for transfer of data to and
from a hard disk. It is the successor to the legacy AT Attachment standard (ATA). This older
technology was retroactively renamed Parallel ATA (PATA) to distinguish it from Serial ATA.
Both SATA and PATA drives are IDE (Integrated Drive Electronics) drives, although IDE is
often misused to indicate PATA drives.
The two SATA interfaces, SATA/150, runs at 1.5 GHz resulting in an actual data transfer rate of
1.2 Gigabits per second (Gb/s), or 150 megabytes per second (MB/s). SATA II 3Gb/s resulting in
an actual data transfer rate of 2.4 Gb/s, or 300 MB/s.
Motherboard Slots
To add more functionality to a computer, cards such as network or video cards can be added.
Sometimes these functions are built into the motherboard. There are several types of expansion
slots:
The PCI (Peripheral Component Interconnect) The PCI bus is common in modern PCs, where it
has displaced ISA as the standard expansion bus, but it also appears in many other computer
types.
PCI 2 33.33 MHz clock with synchronous transfers peak transfer rate of 133 MB per second for
32-bit bus
PCI 2.2 allows for 66 MHz signalling (requires 3.3 volt signalling) (peak transfer rate of 503
MB/s) PCI 2.3 permitted use of 3.3 volt and universal keying, but did not support 5 volt keyed
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add in cards.
PCI 3.0 is the final official standard of the bus, completely removing 5 volt support.
ISA/EISA; Industry Standard Architecture and Extended Industry Standard Architecture An
older type of bus connector. Considered obsolete
PCI Express, PCIe, or PCI-E is an implementation of the PCI computer bus that uses existing
PCI programming concepts, but bases it on a completely different and much faster serial
physical-layer communications protocol. PCIe transfers data at 250 MB/s (238 MiB/s), per
channel to a maximum of 16 channels, a total combined transfer rate of 4GB/s (3.7 GiB/s).
Almost all of the high end graphics cards being released today use PCI Express. NVIDIA uses
the high-speed data transfer of PCIe for its newly developed Scalable Link Interface (SLI)
technology, which allows two graphics cards of the same chipset and model number to be run at
the same time, allowing increased performance.
The Accelerated Graphics Port (also called Advanced Graphics Port) is a high-speed point-topoint channel for attaching a graphics card to a computer’s motherboard, primarily to assist in
the acceleration of 3D computer graphics. Some motherboards have been built with multiple
independent AGP slots. AGP is slowly being phased out in favour of PCI Express.
AGP 1x, using a 32-bit channel operating at 66 MHz resulting in a maximum data rate of 266
megabytes per second (MB/s), doubled from the 133 MB/s transfer rate of PCI bus 33 MHz / 32bit; 3.3 V signaling.
AGP 2x, using a 32-bit channel operating at 66 MHz double pumped to an effective 133 MHz
resulting in a maximum data rate of 533 MB/s; signaling voltages the same as AGP 1x;
AGP 4x, using a 32-bit channel operating at 66 MHz quad pumped to an effective 266 MHz
resulting in a maximum data rate of 1066 MB/s (1 GB/s); 1.5 V signaling;
AGP 8x, using a 32-bit channel operating at 66 MHz, strobing eight times per clock, delivering
an effective 533 MHz resulting in a maximum data rate of 2133 MB/s (2 GB/s); 0.8 V signaling.
Peripheral Connections
There are a number of ports on the motherboard for the connection of additional devices:.
Serial ports connected the computer to devices such as terminals or modems. Mice, keyboards,
and other peripheral devices also connected in this way.
Parallel ports are most often used to communicate with peripheral devices. The most common
kind of parallel port is a printer port, such as a Centronics connector based port which transfers
eight bits at a time. Disk drives are also connected via special parallel ports, such as those used
by the SCSI and ATA technlogies. However, when people refer to a parallel port, they are
usually referring to a printer port, either on a printer or a PC.
A USB system has an asymmetric design, consisting of a host controller and multiple daisychained devices. Additional USB hubs may be included in the chain, allowing branching into a
tree structure, subject to a limit of 5 levels of branching per controller. No more than 127
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devices, including the bus devices, may be connected to a single host controller. Modern
computers often have several host controllers, allowing a very large number of USB devices to
be connected. USB cables do not need to be terminated.
USB supports three data rates.
A Low Speed rate of 1.5 Mbit/s (183 KiB/s) that is mostly used for Human Interface Devices
(HID) such as keyboards, mice, and joysticks.
A Full Speed rate of 12 Mbit/s (1.5 MiB/s). Full Speed was the fastest rate before the USB 2.0
specification and many devices fall back to Full Speed. Full Speed devices divide the USB
bandwidth between them in a first-come first-served basis and it is not uncommon to run out of
bandwidth with several isochronous devices. All USB Hubs support Full Speed.
A Hi-Speed rate of 480 Mbit/s (57 MiB/s).
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Module 2
Introduction to Networking
1.1 Why use a Network?
Quite simply explained we use networks for communication between computers, sharing of data
and peripherals. In the business world we use networks for ease of administration and to cut
costs.
Sharing data example imagine an office with 5 secretaries working on 5 different computers, one
requires a file from another computer in a non networked office this file would have to be written
to a portable media then loaded onto the computer. In a networked office the file could be
accessed via the network from a shared folder.
Sharing peripherals example the same office with 5 secretaries working on 5 different computers,
in order to print their work each computer would need to have a printer attached. In a networked
office you could have one shared printer, cutting costs.
What do you need?
A common language or protocol (TCP/IP IPX/SPX, APPLE TALK) is a convention or standard
that controls or enables the connection, communication, and data transfer between two
computing endpoints.
A common language or protocol (TCP/IP IPX/SPX, APPLE TALK) is a convention or standard
that controls or enables the connection, communication, and data transfer between two
computing endpoints.
Cabling BNC,Cat5, fibre optic
Hardware NIC(Network Interface Card), router, switch, hub, modem wireless access point.
Network Service (DNS, WINS, DHCP).
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Network Hardware
Network Interface Card
A network card, network adapter, network interface card or NIC is a piece of computer hardware
designed to allow computers to communicate over a computer network. It has a MAC address.
Every network card has a unique 48-bit serial number called a MAC address, which is written to
ROM carried on the card. Every computer on a network must have a card with a unique MAC
address. The IEEE is responsible for assigning MAC addresses to the vendors of network
interface cards. No two cards ever manufactured should share the same address.
Hubs
An Ethernet hub or concentrator is a device for connecting multiple twisted pair or fibre optic
Ethernet devices together, making them act as a single segment. It works at the physical layer of
the OSI model, repeating the signal received at one port out each of the other ports (but not the
original one). The device is thus a form of multiport repeater. Ethernet hubs are also responsible
for forwarding a jam signal to all ports if it detects a collision. Hubs also often come with a BNC
and/or AUI connector to allow connection to legacy 10BASE2 or 10BASE5 network segments.
The availability of low-priced Ethernet switches has largely rendered hubs obsolete but they are
still seen in older installations and more specialist applications.
Switches
A network switch or switch for short is a networking device that performs transparent bridging
(connection of multiple network segments with forwarding based on MAC addresses) at full wire
speed in hardware. As a frame comes into a switch, the switch saves the originating MAC
address and the originating (hardware) port in the switch’s MAC address table. This table often
uses content-addressable memory, so it is sometimes called the “CAM table”. The switch then
selectively transmits the frame from specific ports based on the frame’s destination MAC
address and previous entries in the MAC address table. If the destination MAC address is
unknown, for instance, a broadcast address or (for simpler switches) a multicast address, the
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switch simply transmits the frame out of all of the connected interfaces except the incoming port.
If the destination MAC address is known, the frame is forwarded only to the corresponding port
in the MAC address table.
Hubs VS Switches
A hub, or repeater, is a fairly unsophisticated broadcast device. Any packet entering any port is
broadcast out on every port and thus hubs do not manage any of the traffic that comes through
their ports. Since every packet is constantly being sent out through every port, this results in
packet collisions, which greatly impedes the smooth flow of traffic. A switch isolates ports,
meaning that every received packet is sent out only to the port on which the target may be found
(assuming the proper port can be found; if it is not, then the switch will broadcast the packet to
all ports except the port the request originated from). Since the switch intelligently sends packets
only where they need to go the performance of the network can be greatly increased.
Routers
A router is a computer networking device that forwards data packets across a network toward
their destinations, through a process known as routing. A router acts as a junction between two or
more networks to transfer data packets among them. A router is different from a switch. A switch
connects devices to form a Local area network (LAN).
One easy illustration for the different functions of routers and switches is to think of switches as
local streets, and the router as the junctions with the street signs. Each house on the local street
has an address within a range on the street. In the same way, a switch connects various devices
each with their own IP address(es) on a LAN. Routers connect networks together the way that
on-ramps or major junctions connect streets to both main roads and motorways. The street signs
at the junctions the (routing table) show which way the packets need to flow.
Wireless
Wireless Access Point (WAP) A wireless access point (AP) connects a group of wireless stations
to an adjacent wired local area network (LAN). An access point is similar to an Ethernet hub, but
instead of relaying LAN data only to other LAN stations, an access point can relay wireless data
to all other compatible wireless devices as well as to a single (usually) connected LAN device, in
most cases an Ethernet hub or switch, allowing wireless devices to communicate with any other
device on the LAN.
Wireless Routers A wireless router integrates a wireless access point with an Ethernet switch and
an Ethernet router. The integrated switch connects the integrated access point and the integrated
Ethernet router internally, and allows for external wired Ethernet LAN devices to be connected
as well as a (usually) single WAN device such as a cable modem or DSL modem. A wireless
router advantageously allows all three devices (mainly the access point and router) to be
configured through one central configuration utility, usually through an integrated web server.
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However one disadvantage is that one may not decouple the access point so that it may be used
elsewhere.
Cables
Cable Terminology
10BASE2 (also known as cheapernet or thinnet) is a variant of Ethernet that uses thin coaxial
cable. The 10 comes from the maximum transmission speed of 10 Mbit/s (millions of bits per
second). The BASE stands for baseband signaling, and the 2 represents a rounded up shorthand
for the maximum segment length of 185 metres (607 feet).
10BASE5 (also known as thicknet) is the original “full spec” variant of Ethernet cable. The 10
refers to its transmission speed of 10 Mbit/s. The BASE is short for baseband signalling as
opposed to broadband, and the 5 stands for the maximum segment length of 500 metres.
10BASE-T is an implementation of Ethernet which allows stations to be attached via twisted pair
cable. The name 10BASE-T is derived from several aspects of the physical medium. The 10
refers to the transmission speed of 10 Mbit/s. The BASE is short for baseband.The T comes from
twisted pair, which is the type of cable that is used
100BASE-T is any of several Fast Ethernet 100 Mbit/s CSMA/CD standards for twisted pair
cables, including: 100BASE-TX (100 Mbit/s over two-pair Cat5 or better cable). The segment
length for a 100BASE-T cable is limited to 100 metres
Coaxial
Coaxial cable is an electrical cable consisting of a round conducting wire, surrounded by an
insulating spacer, surrounded by a cylindrical conducting sheath, usually surrounded by a final
insulating layer. It is used as a high-frequency transmission line to carry a high-frequency or
broadband signal.
BNC connectors were commonly used on 10base2 thin Ethernet networks, both on cable
interconnections and network cards; though these have largely been replaced by newer Ethernet
devices whose wiring does not use coaxial cable.
CAT 5
Category 5 cables: commonly known as Cat 5, is an unshielded twisted pair cable type designed
for high signal integrity. Category 5 has been superseded by the Category 5e specification. This
type of cable is often used in structured cabling for computer networks such as Gigabit Ethernet,
although they are also used to carry many other signals such as basic voice services, token ring.
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Category 5 cable included four twisted pairs in a single cable jacket. It was most commonly used
for 100 Mbit/s networks, such as 100BASE-TX Ethernet
Cat5 cable uses an RJ-45 (Registered Jack-45) connector at each end of the cable with a fixed
wiring scheme. The ends are then crimped on to the cable
Wiring Scheme
Patch or straight through cables have Wiring scheme 1 at both ends of the cable and are used to
connect computers to network wall sockets or hubs.
Crossover cables have Wiring scheme 1 at one end of the cable and Wiring scheme 2 at the
other. These cables are used to connect network hardware together e.g. PC to PC, hub to hub.
Protocols
A protocol (TCP/IP IPX/SPX, APPLE TALK) is a convention or standard that controls or
enables the connection, communication, and data transfer between two computing endpoints.
Sending and receiving systems need to use the same protocol unless a gateway service sits
between networks and translates from one to the other.
Most protocols specify one or more of the following properties:






Detection of the underlying physical connection (wired or wireless), or the existence of
the other endpoint or node
Handshaking
Negotiation of various connection characteristics
How to start and end a message
How to format a message
What to do with corrupted or improperly formatted messages (error correction)
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

How to detect unexpected loss of the connection, and what to do next
Termination of the session or connection
NetBIOS
NetBIOS is an acronym for Network Basic Input/Output System. The NetBIOS API allows
applications on separate computers to communicate over a local area network. NetBIOS must be
enabled for Windows File and Print Sharing to work.
NetBIOS provides three distinct services:



Name service for name registration and resolution
Session service for connection-oriented communication
Datagram distribution service for connectionless communication.
Name service In order to start Sessions or distribute Datagrams, an application must register its
NetBIOS name using the Name service. NetBIOS names are 16 bytes in length
Session service Session mode lets two computers establish a connection for a “conversation,”
allows larger messages to be handled, and provides error detection and recovery. In NBT, the
session service runs on TCP port 139.
Datagram distribution service Datagram mode is “connectionless”. Since each message is sent
independently, they must be smaller; the application becomes responsible for error detection and
recovery. In NBT, the datagram service runs on UDP port 138.
IPX/SPX (NWLINK)
Internetwork Packet Exchange (IPX) is the OSI-model Network layer protocol in the IPX/SPX
protocol stack. The IPX/SPX protocol stack is supported by Novell’s NetWare network
operating system. Because of Netware’s popularity through the late 1980s into the mid 1990s,
IPX became a popular internetworking protocol. Novell derived IPX from Xerox Network
Services’ IDP protocol. IPX usage is in general decline as the boom of the Internet has made
TCP/IP nearly universal. Computers and networks can run multiple network protocols, so almost
all IPX sites will be running TCP/IP as well to allow for Internet connectivity. It is also now
possible to run Novell products without IPX, as they have supported both IPX and TCP/IP since
NetWare reached version 5.
Sequenced Packet Exchange (SPX) is a transport layer protocol (layer 4 of the OSI Model) used
in Novell Netware networks. The SPX layer sits on top of the IPX layer (layer 3 – the network
layer) and provides connection-oriented services between two nodes on the network. SPX is used
primarily by client/server applications.
NWLink is a IPX/SPX-compatible protocol developed by Microsoft and used in its Windows NT
product line. NWLink is Microsoft’s version of Novell’s IPX/SPX Protocol. The Microsoft
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version of NWLink includes the same level of functionality as the Novell Protocol. NWLink
includes a tool for resolving NetBIOS names. NWLink packages data to be compatible with
client/server services on NetWare Networks. However, NWLink does not provide access to
NetWare File and Print Services. To access the File and Print Services the Client Service for
NetWare needs to be installed.
AppleTalk
AppleTalk is a suite of protocols developed by Apple Computer for computer networking. It was
included in the original Macintosh (1984) and is now used less by Apple in favour of TCP/IP
networking.
AppleTalk contains two protocols aimed at making the system completely self-configuring. The
AppleTalk address resolution protocol (AARP) allowed AppleTalk hosts to automatically
generate their own network addresses, and the Name Binding Protocol (NBP) was essentially a
dynamic DNS system which mapped network addresses to user-readable names.
For interoperability Microsoft maintains the file services for Macintosh and the print services for
Macintosh
TCP/IP
The Internet protocol suite is the set of communications protocols that implement the protocol
stack on which the Internet and most commercial networks run. It is sometimes called the
TCP/IP protocol suite, after the two most important protocols in it: the Transmission Control
Protocol (TCP) and the Internet Protocol (IP), which were also the first two defined. The Internet
protocol suite like many protocol suites can be viewed as a set of layers; each layer solves a set
of problems involving the transmission of data, and provides a well-defined service to the upper
layer protocols based on using services from some lower layers. Upper layers are logically closer
to the user and deal with more abstract data, relying on lower layer protocols to translate data
into forms that can eventually be physically transmitted. The OSI model describes a fixed, seven
layer stack for networking protocols. Comparisons between the OSI model and TCP/IP can give
further insight into the significance of the components of the IP suite, but can also cause
confusion, as TCP/IP consists of only 4 layers.
The four layers in the DoD model, from bottom to top, are:


The Network Access Layer is responsible for delivering data over the particular hardware
media in use. Different protocols are selected from this layer, depending on the type of
physical network.
The Internet Layer is responsible for delivering data across a series of different physical
networks that interconnect a source and destination machine. Routing protocols are most
closely associated with this layer, as is the IP Protocol, the Internet’s fundamental
protocol.
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

The Host-to-Host Layer handles connection rendezvous, flow control, retransmission of
lost data, and other generic data flow management. The mutually exclusive TCP and
UDP protocols are this layer’s most important members.
The Process Layer contains protocols that implement user-level functions, such as mail
delivery, file transfer and remote login.
Network Services
DNS (Domain Naming System)
The Domain Name System (DNS) stores and associates many types of information with domain
names, but most importantly, it translates domain names (computer hostnames) to IP addresses.
It also lists mail exchange servers accepting e-mail for each domain. In providing a worldwide
keyword-based redirection service, DNS is an essential component of contemporary Internet use.
The DNS pre-eminently makes it possible to attach easy-to-remember domain names (such as
“es-net.co.uk”) to hard-to-remember IP addresses (such as 270.146.131.206). People take
advantage of this when they recite URLs and e-mail addresses.
WINS (Windows Internet Naming Service)
Windows Internet Naming Service (WINS) is Microsoft’s implementation of NetBIOS Name
Server (NBNS) on Windows, a name server and service for NetBIOS computer names.
Effectively, it is to NetBIOS names what DNS is to domain names – a central mapping of host
names to network addresses. However, the mappings have always been dynamically updated
(e.g. at workstation boot) so that when a client needs to contact another computer on the network
it can get its up-to-date DHCP allocated address. Networks normally have more than one WINS
server and each WINS server should be in push pull replication; the favoured replication model
is the hub and spoke, thus the WINS design is not central but distributed. Each WINS server
holds a full copy of every other related WINS system’s records. There is no hierarchy in WINS
(unlike DNS), but like DNS its database can be queried for the address to contact rather than
broadcasting a request for which address to contact. The system therefore reduces broadcast
traffic on the network, however replication traffic can add to WAN / LAN traffic.
DHCP (Dynamic Host Configuration Protocol)
The Dynamic Host Configuration Protocol (DHCP) automates the assignment of IP addresses,
subnet masks, default routers, and other IP parameters. The assignment usually occurs when the
DHCP configured machine boots up or regains connectivity to the network. The DHCP client
sends out a query requesting a response from a DHCP server on the locally attached network.
The DHCP server then replies to the client with its assigned IP address, subnet mask, DNS server
and default gateway information. The assignment of the IP address usually expires after a
predetermined period of time, at which point the DHCP client and server renegotiate a new IP
address from the server’s predefined pool of addresses. Configuring firewall rules to
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accommodate access from machines who receive their IP addresses via DHCP is therefore more
difficult because the remote IP address will vary from time to time. Administrators must usually
allow access to the entire remote DHCP subnet for a particular TCP/UDP port. Most home
routers and firewalls are configured in the factory to be DHCP servers for a home network. ISPs
(Internet Service Providers) generally use DHCP to assign clients individual IP addresses. DHCP
is a broadcast-based protocol. As with other types of broadcast traffic, it does not cross a router.
APIPA (Automatic Private IP Addressing)
If computers are unable to pick an address up from a DHCP server they use Automatic Private IP
Addressing (APIPA). This means the computer will assign itself a random address between
169.254.0.1 – 169.254.254.254/16, allowing it to communicate with other clients who are also
using APIPA.
Automatic Private IP Addressing (APIPA), this allows unknowledgeable users to connect
computers, networked printers, and other items together and expect them to work. Without
Zeroconf or something similar, a knowledgeable user must either set up special servers, like
DHCP and DNS, or set up each computer by hand.
Networks
A Local Area Network (LAN) is a computer network covering a small local area, like a home,
office, or small group of buildings such as a home, office, or college. Current LANs are most
likely to be based on switched Ethernet or Wi-Fi technology running at 10, 100 or 1,000 Mbit/s.
The defining characteristics of LANs in contrast to WANs (wide area networks) are: their much
higher data rates; smaller geographic range; and that they do not require leased
telecommunication lines.
A Personal Area Network (PAN) is a computer network used for communication among
computer devices (including telephones and personal digital assistants) close to one person. The
reach of a PAN is typically a few metres and may use Bluetooth, wireless or USB for
connection.
A Wide Area Network (WAN) is a computer network covering a wide geographical area,
involving a vast array of computers. This is different from personal area networks (PANs),
metropolitan area networks (MANs) or local area networks (LANs) that are usually limited to a
room, building or campus. The most well-known example of a WAN is the Internet. WANs are
used to connect local area networks (LANs) together, so that users and computers in one location
can communicate with users and computers in other locations.
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